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Species · Maryland · BBS 2025 Release · 1966–2024

Black-crowned Night Heron Population Trend in Maryland

All statesWetland birds

Black-crowned Night Heron in Maryland has fallen sharply: down 75% on the route-weighted index since 1975.

-75%Since 1975TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
14Routes In StateSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
29YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Black-crowned Night Heron Trends in MarylandNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

long arc declinecomputed indexTrend sourceWhether the figure is our own computed route-weighted index or an official USGS modeled estimate. The current build labels every trend as computed.Full methodology →

Black-crowned Night Heron has fallen sharply in Maryland: down 75% on the route-weighted index since 1975.

Black-crowned Night Heron Population Forecast in Maryland

If the recent trend holds, Black-crowned Night Heron in Maryland is projected to stay roughly flat through 2029, near 0.00 (95% range 0.00–0.25). A 5-year backtest shows a typical error of ±361.4%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2029TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
0.00Projected 2029 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.2595% range95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
±361.4%Backtest errorBacktest errorTypical error when we hold out the most recent years, forecast them, and compare to what actually happened. Lower means a more trustworthy projection.Full methodology →
If the recent trend holds, Black-crowned Night Heron in Maryland is projected to stay roughly flat through 2029, near 0.00 (95% range 0.00–0.25). A 5-year backtest shows a typical error of ±361.4%, with 100% of held-out values landing inside the 95% band.19732029
Projection of the recent trend (dashed) with 80/95% bands — a projection, not a prediction. Habitat, climate, and land use are not modeled.
YearProjected indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →95% low95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →95% high95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
20250.000.000.25
20260.000.000.25
20270.000.000.25
20280.000.000.25
20290.000.000.25

Black-crowned Night Heron Survey Routes in Maryland

Routes recording Black-crowned Night Heron in Maryland.
Recent countThe raw number of individuals recorded on this route in its most recent survey year. A single-route tally, not a trend.Full methodology →
Sinepuxent319771973
Elkton219961982
Fruitland219831974
Newark219761976
Ijamsville220232007
Walnut220192019
Theodore120101973
Williamsport120152015
Honga119741974
Olney120242024
Madison120082008
Wheaton120242022
Berlin119911991
Pomfret119981997

Black-crowned Night Heron Population Trend in Other States

alabamaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22.